Vehicular tires typically have treads of rubber compositions comprised of selected elastomers and particulate reinforcing fillers.
Such elastomers may typically include cis 1,4-polybutadiene rubber to promote, for example, resistance to treadwear, styrene/butadiene rubber to promote, for example, wet traction and sometimes natural rubber to promote, for example, heat durability for the tire tread. Sometimes functionalized elastomers have been proposed such as, for example amine and siloxy functionalized styrene/butadiene rubbers. For example, see U.S. Pat. No. 7,816,483.
For this invention, however, an emphasis is placed on providing a tire tread which might be suitable, for example, for a tire in which tread traction (e.g. skid resistance) is most important and resistance to tread wear is of lesser importance such as, for example, for a vehicle which may be desired to travel at relatively high speeds.
For such purpose, it is proposed that the rubber composition be exclusive of any appreciable amount of, and preferably exclusive of, cis 1,4-polybutadiene rubber and natural rubber.
For such purpose, it is proposed that a rubber composition for a tire tread be evaluated for which its elastomer constituent is limited to a functionalized elastomer such as, for example, a carboxylated nitrile rubber (x-NBR) or carboxylated styrene/butadiene rubber (x-SBR).
In the description of this invention, the terms “rubber” and “elastomer” if used herein, may be used interchangeably, unless otherwise prescribed. The terms “rubber composition”, “compounded rubber” and “rubber compound”, if used herein, are used interchangeably to refer to “rubber which has been blended or mixed with various ingredients and materials” and such terms are well known to those having skill in the rubber mixing or rubber compounding art.
The term “phr” where used herein, and according to conventional practice, refers to “parts of a respective material per 100 parts by weight of rubber, or elastomer”.
The Tg of an elastomer, if referred to herein, refers to an onset glass transition temperature of the rubber which can conveniently be determined by a differential scanning calorimeter at a heating rate of 10° C. per minute. For example, see ASTM D-1356-98.
A softening point of a resin, where appropriate, is determined by “Ring and Ball” ASTM No. E28.